JP-A-8-50922 proposes a negative electrode for a lithium secondary battery containing, as constituent components, a metal element that forms an alloy with lithium and a metal element that does not form an alloy with lithium, in which the content of the metal element that does not form an alloy with lithium is higher in the surface portion that is to come into contact with an electrolyte and to face the positive electrode and in the portion that leads to an output terminal. The publication alleges that electroconductivity is maintained via the metal that does not form a lithium alloy even though the metal that forms a lithium alloy pulverizes due to charge/discharge cycling.
The embodiments suggested in JP-A-8-50922 include a structure composed of a current collecting member made of a metal that does not form a lithium alloy and a member made of powder containing a metal element that forms a lithium alloy, in which the latter member is adhered to the former member with a binder. The structure may be fired. It is also suggested to dispose a metal element that does not form a lithium alloy on the layer containing a metal that forms a lithium alloy. The metal element that does not form a lithium alloy is provided by, for example, plating.
However, the negative electrode of JP-A-8-50922 fails to be covered with the metal incapable of forming a lithium alloy at a sufficient coverage and to have sufficient strength because the layer of the metal incapable of forming a lithium alloy is very thin as about 50 nm in thickness. As a result, the negative electrode is incapable of sufficiently accommodating the stress created by volumetric change of the active material due to expansion and contraction accompanying alternate charging and discharging. Noticeable deformation of the negative electrode will thus result. When the active material pulverizes through expansion and contraction, the negative electrode is incapable of effectively preventing the active material from falling off. Therefore, it is still difficult with this technique to provide a negative electrode with improved cycle characteristics.
Apart from JP-A-8-50922, a negative electrode for nonaqueous secondary batteries in which an active material layer has through-holes has been proposed (see JP-A-2001-76761). In a case when the active material pulverizes through its expansion and contraction, however, the proposed negative electrode has difficulty in maintaining electroconductivity and preventing the active material from falling off the side wall of the through-holes. Therefore, it is not easy to obtain improved cycle characteristics with that structure.